1. Field of the Invention
The present invention relates to a machine tool and a machining method thereof, especially a machine tool having a servo motor moving a tool supporting member, and a servo driver driving the servo motor.
2. Description of the Prior Art
It is well known that there are several machine tools controlling a servo motor to move a wheel slide (defined as a “tool supporting member” here) by a servo motor, for example that disclosed in laid-open patent publication Tokkai 2005-327191. In this disclosed prior machine tool, a feedback control is executed by detecting a position of the tool supporting member such as by a rotational angle of the servo motor or a linear position of a linear scale. Namely, the feedback control is executed by the position of the tool supporting member so that tool supporting member is moved to a desired position by the feedback control of the position of the tool supporting member.
A tool or a workpiece machined by the tool is slightly deformed to be bent by machining stress because of its flexibility. Also, there is some thermal distortion in the tool or the workpiece by machining. Any influence by the deformation or the thermal distortion of the tool or the workpiece can not removed by the feedback control in the prior art. Therefore, a higher accuracy machining of the workpiece can be achieved by checking these influences.
It is also well known that there are several machine tools having a sizing device measuring a diameter of the workpiece, for example measuring an inner diameter, as disclosed in another laid-open patent publication Tokkai 2005-279882. In this another prior art, it is disclosed that a process change is performed at a timing determined by an inner diameter of the workpiece measured by the sizing device. The process is changed when a measured value by the sizing device reaches a predetermined value. For example, it is changed from a rough grinding process to a precise grinding process or from a precise grinding process to a finish grinding process.
Inventors of the present invention conceived that machining in consideration of these influences, including the slight deformation or the thermal distortion of the tool or the workpiece, is performed by driving the servo motor on the basis of information measured by the sizing device in order to achieve more precise machining. Inventors of the present invention also conceived to be able to achieve a higher responsiveness of driving the servo motor on the basis of the measured information by the sizing device than that executing the feedback control by detecting information of the position detector, such as the linear scale, etc.
However, the sizing device in the prior art has a construction to output a signal only when the sizing value reaches to the predetermined value because of its purpose to change these processes.